At present drilling mud is prepared by mixing clay powder with water either in mechanical mixers, jet-cutting mills and hydrojet mixers exhibiting a sufficient stirring capacity but low performance and efficiency of dispersing action, or in magnetostriction apparatus which exhibit high performance but also have a low efficiency of dispersion of solid phase "Driller's Handbook" by V. I. Mischevich, N. A. Sidorov, vol. 1, published 1973, Nedra Publishers, Moscow, pp. 359-367 (in Russian).
Dispersion of solid phase of drilling mud is an important production step in the preparation of drilling mud since it substantially improves quality of the drilling mud and reduces the consumption of clay powder, weighing compound and chemicals.
Known in the art are various apparatus for the preparation of drilling mud by dispersing solid phase, such as bead mills, comprising a milling chamber accommodating a shaft, plates and milling bodies. These apparatus are, however, rather unproductive, they are inconvenient in operation and exhibit rapid wear of milling bodies (USSR Inventor's Certificates Nos. 447.497, 447.498 published in Bull. "Discoveries, Inventions, Industrial Designs and Trademarks", No. 39, 1974, IPC, E21B, 11/00).
Known in the art is an apparatus for the preparation of drilling mud, comprising a closed vessel having inlet and outlet pipes and accommodating a piston which is arranged between perforated plates (USSR Inventor's Certificate No. 438.433, published in Bull. "Discoveries, Inventions, Industrial Designs and Trademarks", No. 29, 1975, IPC B01F, 11/00).
Drilling mud is prepared in this apparatus by stirring the components during the piston movement. A dispersing action is not, however, ensured in this apparatus since the intensity of destruction of compacted aggregates of solid phase is low due to a constant pressure of materials being mixed. In addition, the apparatus required the use of a special pump thus increasing power requirements and cost.
The main object of the present invention is to provide a method and an apparatus for preparation of drilling mud which owing to an efficient dispersing action ensure the intensity of physico-chemical exchange process while substantial lowering power requirements and cost.
The invention resides in that in a method for the preparation of drilling mud, comprising mixing solid and liquid phases of drilling mud to obtain a homogeneous suspension, according to the invention, drilling mud is caused to pass under pressure, after the mixing, through apertures of a diameter which is greater than maximum size of an individual solid phase particle but smaller than the diameter of aggregates of such particles, to prepare dispersed drilling mud.
The method according to the invention enables an improvement of intensity of dispersing action owing to the throttling of a mixture which results in a commminution of solid phase particles due to turbulization and cavitation occurring when the flow of drilling mud passes through the apertures.
pH of the drilling mud is preferably caused to grow simultaneously with the passage of the drilling mud through the apertures. An increase in pH (that is alkalinity) of drilling mud improves the conditions for dispersing solid phase.
pH of drilling mud is preferably caused to grow by means of a unipolar electric treatment of drilling mud thus eliminating the influence of noxious oxidation products in the zone of negative electrode, improving the intensity of physico-chemical exchange processes and contributing to an improvement of the efficiency of dispersing action.
The method disclosed in the present invention is preferably carried out in an apparatus comprising a vessel for stirring solid and liquid phases of drilling mud, having inlet and outlet openings and a stirring member accommodated in the vessel and connected to a drive by means of a rod, wherein, according to the invention, the stirring member comprises at least one piston with calibrated apertures of a diameter which is greater than maximum size of an individual solid phase particle but smaller than the diameter of aggregates of such particles.
This arrangement of the apparatus enables an improvement of the intensity of dispersing action on solid phase and reduction of cost of the preparation of drilling mud since the stirring member also functions as a pump.
The apparatus is preferably provided with at least one additional pistion which is mounted in the vessel for movement in opposition to the first piston. This arrangement enables an increase in impact and abrading forces applied to solid phase and also an increase in the pressure difference in the medium being dispersed.
The additional piston is preferably made also with calibrated apertures of a diameter which is greater than maximum size of an individual solid phase particle but smaller than the diameter of aggregates of such particles so that individual particles can pass through the apertures and aggregates are comminuted into finer parts upon collision of the pistons.
The apertures of one piston are preferably misaligned with respect to the apertures of the additional piston so as to intensify the turbulization of drilling mud flow by bending it.
Total area of the calibrated apertures of each piston is preferably equal to or smaller than the surface area of the remaining part of the piston between the apertures.
This arrangement of the pistons enables the creation of pressure difference in the spaces between and behind the pistons during their relative movement thus intensifying turbulization of liquid jets passing the apertures.
The apparatus is preferably provided with one positive electrode and another negative electrode which are separated by means of a semipermeable partition defining two chambers of which one chamber accommodating the negative electrode is designed for the preparation of finished drilling mud and the other chamber is designed for accumulating products of oxidation reactions which are formed upon passing electric current through drilling mud. A direct current source is provided which has the negative terminal connected to at least one piston and the positive terminal connected to a wall of the vessel through which extends the rod of this piston, at least one semipermeable partition being provided adjacent to this wall to define with the wall a chamber for accumulating products of oxidation reactions which are formed when electric current is passed through drilling mud the partition being made of a material hindering the penetration of products of oxidation reactions to the remaining part of the vessel.
This arrangement of the apparatus enables an increase in pH (alkalinity) of drilling mud during dispersion of solid phase in the chamber for the preparation of finished drilling mud, and the provision of chambers for accumulating products of oxidation reactions enables the prevention of the penetration of such products to the negative electrode zone where an electric treatment of drilling mud is effected.
Therefore, the method and apparatus according to the invention make it possible to prepare finely dispersed drilling mud, that is quality of drilling mud being produced is substantially improved, and both power requirements and cost are lowered.